Embryonic stem cells (ES cells) are stem cells established from early embryos of human or mice. ES cells are pluripotent, being capable of differentiating into all cells in the body. At the current time, human ES cells are usable in cell transplantation therapy for numerous diseases including Parkinson's disease, juvenile onset diabetes and leukemia. However, barriers exist against transplantation of ES cells. In particular, transplantation of ES cells can provoke immunorejection similar to the rejection encountered after unsuccessful organ transplantation. Moreover, there are many ethical considerations as well as critical and dissenting opinions against the use of ES cell lines that have been established by destruction of human embryos.
It was against this background that Professor Shinya Yamanaka of Kyoto University was successful in establishing induced pluripotent stem cells (iPS cells) by transferring four genes: Oct3/4, Klf4, c-Myc and Sox2, into somatic cells. For this, Professor Yamanaka received the Nobel Prize in Physiology or Medicine in 2012 (see PTL 1, for example). iPS cells are ideal pluripotent cells free of the issues of rejection or ethical problems. Therefore, iPS cells are considered promising for use in cell transplantation therapy.